1. Technical Field of the Invention
This invention includes one micro-cavity measuring method and two items of detecting equipment based on micro focal-length collimation, which can be used for measurement of irregular micro-cavities and “sub-macro” micro-cavities in particular, in addition to conventional contact measurement.
2. Technical Background
Miniaturization is one of the most important development trends in many application fields, such as the aviation industry, electronic industry, and medical instruments, etc. Products with micro-cavities features have great importance in applications, such as fuel injector nozzles, inertial instruments, fiber optic ferrules, wire drawing dies, holes in printed circuit boards and medical apparatus, etc. Limited by the micro space and the measuring force, it's difficult to measure micro-cavities with high aspect ratio and high precision. Detectors with slim probes have been designed mainly for measurement of micro-cavities in different kinds of modes. Coordinate measuring mechanisms (CMM) are combined with these detectors to complete the measurement of micro-cavities in aiming and triggering modes. CMM technologies have been developed well to realize precise three-dimensional (three dimensional) movement with nanometer uncertainties, but micro-cavities detectors have not. Most of these detectors have sub-micrometer uncertainties only.
Yang Shimin , Li Shuhe , Han Meimei ,et al. have invented a detector for the measurement of holes of 200 μm in diameter with an accuracy of approximately 1 μm. Its probe is modeled as an elastic body so that the deflections of the body can be sensed using capacitance sensors. This method has a nonlinear error of 0.2 μm caused by the detecting process, and its probe is difficult to be miniaturized further. B. J. Kim, T. Masuzawa and T. Bourouina et al. have invented a vibrating-scanning method for measuring micro holes. This method uses a vibrating micro probe that contacts an electrically conducting surface. Upon contact, the circuit closes, thus sending out a signal. The signal is intermittent as the probe is vibrating. The duration of contact with the surface in relation to the time for one amplitude of probe vibration provides an index of proximity of the probe to the surface. Masuzawa refined this technique using a twin probe to measure non-conducting surfaces as well. The vibrating-scanning technology is capable of measuring hole diameter of approximately 125 μm with an accuracy of 0.5 μm. This method has a big drift caused by the vibrated source, and the probe tip shape is rectangle, which causes a blind spot error.
H. Schwenke, F. Wäldele, C. Weiskirch, H. Kunzmann et al. have invented a method of imaging a fiber probe's tip for detecting micro holes. A thin fiber of 15 μm in diameter with a ball of 25 μm in diameter on the end is used as the probe. Light enters through the fiber and is incident on the ball. The back scattered light is imaged using a charge coupled device (CCD) camera. This method has sub-micrometer uncertainties to measure holes of approximately 50 μm in diameter. However, this probe can't detect high aspect ratio holes because of the decrease of the back scattered light.
Tan Jiubin and Cui Jiwen have invented a double fibers coupling method for measurement of micro-cavities. Two fibers are coupled with a ball which is used as the probe ball. Light enters through one fiber and is incident in the ball. Some of the back scattered light is transmit by the other fiber and is imaged by a zoom-in lens group to a CCD camera. This method has solved the problems of detecting high aspect ratio holes and has sub-micrometer uncertainties, but its manufacturing process is so hard to be miniaturized further.
B. Muralikrishnan, J. A. Stone, J. R. Stoup et al. have invented an imaging fiber stem method for measurement of micro holes. A thin fiber of 50 μm in diameter with a ball of 75 μm in diameter on the end is used as the probe. The fiber stem is imaged to be a band shape by two same orthogonal optic systems for two-dimensional (two dimensional) monitoring. The optic system has a magnification of 35.A 4 nm uncertainty was achieved roughly in detecting the position of the probe in space under ideal conditions, and an expanded uncertainty of 0.07 μm (k=2) on diameter was got for nominal diameter of 100 μm holes. The measuring depth reaches to 5 mm. This method is better than others, but its imaging magnification is too low to get a more sensitive and faster detecting signal.
A. Kung, F. Meli and R. Thalmann et al. have invented a touch probe based on a parallel kinematic structure of flexure hinges to minimize the moving mass and ensure an isotropic low stiffness. The feature of this probe head supports exchangeable probes down to 0.1 mm in diameter. A repeatability of 5 nm and an uncertainty of 0.05 μm were achieved. This method has a very complex sensing form, and its probe has a miniaturization problem.
Above all, fiber probes have several applications for measurement of micro-cavities and become more suitable for its optical and mechanical features of optical conductivity, easy miniaturization and tiny measuring force. Different methods have been designed for sensing the movements of the fiber probe, and the followings are some of its drawbacks:    1. The detecting resolutions of the fiber probes are hard to be enhanced further. Most of the fiber probes have sub-micrometer resolutions only. The movement sensitivities of detecting the fiber probes are too low;    2. There is no absolute zero point, which has interferences to the measuring repeatability and judging measuring polarities;    3. The detector is too complex in construction for general applications;    4. The measuring speed is too low to realize a real-time application.